Shock absorbing structure for airplane landing gears



Ma'rch 3, 1942. G, M, MAGRUM 2,275,371

SHOCK ABsoRBING STRUCTURE vFOR AIRPLANE LANDING-GEARS t Filed June l0, 1938 2 ShStS-Sheet l -E-Elfzo mmm @Ilm/funn L I-mummm# @.lIIIII/llI/l//l/ .FE IUT.'

2 Sheets-Sheet 2 A Mmmm-. '/f 38 n l March 3, 1942. G. M. MAGRUM sHocK AsoRING STRUCTURE FOR AIRPLANE LANDING GEAR's Filed June 1o, 1938 Patented Mar. 3, V194.2

SHOCK ABSORBl-NG STRUCTURE FOR l AIRPLANE LANDING GEARS Gervase M. Magrum, Buialo, N. Y., assgnor to Houde Engineering Corporation, Buffalo, N. Y., a corporation of New York Application June 10, 1938, Serial No. 212,867

A 7 claims. (cl. 244-100) This invention relates to hydraulic shock ab' sorber structure adapted particularly for use in connection with the landing gear of airplanes.

In certain types of airplane landing gears,

especially where a single front wheel functions as a caster, shimmy or wobble of this wheel cannot be tolerated, as it might seriously interfere with ecie'nt and safe landing. It is therelfore the object of this invention to provide improved hydraulic shock absorber structure which will not interfere with the free caster movement of the single front wheel of a landing gear but will function eiciently to check any shimmy or wobble of the wheel so that smooth and proper operation thereof is assured.

- I preferably employ a hydraulic shock absorber of the rotary type comprising a cylinder structure and a wing piston structure and with means controlling the ow of displaced hydraulic uid. In the usual construction of a landing gear, the bearing fork for the caster wheel is secured to or extends from a tubular strut which is ro-l tatably mounted on the landing gear framework for caster movement of the wheel. Such arrangement is disclosed in patents such as Saulnier 2,105,374, January 11, 1938, or in Ronan Patent 1,937,596, December 5, 1933, lor Ayer Patent 2,110,543, March 8, 1938. With such structure, the end of the tubular strut may be adapted tofunction as the cylinder part of the Figure 1 is a front elevation of the lower end of the landing gear which supports the front wheel: Figure 221s a side elevation of the structure shown in Figure 1;

Figure 3 is an enlarged section on plane III- III of Figure 1;

Figure 4 is a section on plane IV--IV of Figure Figure 5 is a s'ection on plane V-V of Figure Flgure 6 is a section on plane VI--VI of Figure Figure '7 is an enlarged section on plane VII- VII of Figure 5;

Figure 8 is an enlarged sectional View of the replenishing valve structure; and

Figure 9 is a plan view of the valve plate.

Referring to Figures l and 2, the reference numeral I0 represents a tubular strut which extends from the landing gear framework F on which it is rotatably mounted in any suitable manner, for example, as disclosed in the kpatents hereinbefore' referred to. Fork arms II extend downwardly from the lower end of the strut and between which the wheel W is journalled. The fork arms II may be integral with the strut I0 or, as show-n, they may extend from a collar I2 having clamping lugs I3 for receiving bolts I4 hydraulic shock absorber structure, and such adaptation constitutes one of the important features of my invention. With such arrangement, the4 shock absorber structure cylinder becomes part of the rotating caster structure, and the piston element for the shock absorber structure will be anchored to the landing gear framework, so that by turning of the cylinder structure with the wheel the hydraulic fluid will be displaced but-its ow will be suitably metered and controlled so that the wheel may properly function but any shimmy or wobble thereof will be checked.

Landing gears are usually arranged so that after landing they may be drawn up against or into the body of the airplane in which position the axis of the shock absorber structure might assume a horizontal of inverted position, and it is therefore another important object of the invention to provide means for preventing the hydraulic fluid from leaving the hydraulic working chambers and to keep these ,chambers at all times lled with the fluid.

The various features of the invention are shown incorporated in the structure disclosed ondche drawings, in which drawings:

so that the collar maybe rigidly clamped to the strut. The collar I2 is shown provided with a circumferentially extending channel I5 receiving a strap I6 connected by a link I'I forming part of the framework F of the landing gear, the strap supporting the lower end of the strut and guiding its rotary movement with the wheel. As shown by Figure 3, the strut at its lower end may be of reduced diameter to provide an abutment shoulder I8 engaged by the flange I9 at the lower end of the collar I-2 so that the bumps ofthe wheel on the ground will be in-greater part communicated directly to the strut I0 and axial displacement of the collar I2 on the strut prevented.

It should be noted that the rotatable tubular strut III, as is conventional practice (see prior Patents Nos. 2,110,543 and 1,937,596), comprises one telescoping member of an oleo strut or shock absorber, the other cooperating and non-rotatable telescoping tubular member 9 being cupped at its upper end and pivotally attached at 8-to a cross member of the landing gear framework F. As shown on Figure 3, the outer endportion of the strut I0 may form the cylinder wall 20 for the hydraulic shock absorber structure. The inner cross Wall 2| within the cylinder wall v20 seats against a shoulder 22 provided within the wall 20,

and from the cross wall diametrically opposite hydraulic abutments or partition walls 23 and 23 extend forwardly, and, as shown, these abutment walls may be integral with the 'cross wall 2|.

One or more pins 24 may beextended through the wall 20 into the wall 2| for locking the walls together. K.

Theouter cross wall 25 fits intoA the cylinder wall 20 and abuts the outer ends of the partition walls 23 and 23', and a clamping ring 26 having threaded engagement with the wall 20 securely clamps the outer wall 25 against the partition Walls and 'holds the inner wall 2| against its seat 22. Pins 21 will lock the outer wa1l'25 against rotary displacement relative to the partition walls 23 and 23. y

` The walls 20, 2|, and 25 define a. cylinder space for the hydraulic working fluid into which space the partition walls 23 and 23' project radially. Within the cylinder space is the cylindrical hub 28 of the piston structurathe hub bearing against the inner faces of the partition walls and having oppositely extending piston vanes 29 and 29 thereon which engage with the cylindrical inner surface of the wall 20 between the partition walls. The piston shaft 30 extends from the hub 28 through the outer wall 25 and the bearing extenthe diagonally opposite hydraulic working cham-V bers 33 and 33', and the diagonally opposite working chambers 34 and 34'. The piston shaft and its hub have the bore 35 extending therethrough, the inner end of which is enlarged to receive the bearing plug 36 seated in the wall 2|, the plug being hollow and with the enlarged bore end forming a chamber 31 which communicates with the working chambers 33 and 33 through the passages 38 and'38' respectively extending through the piston hub.

Adjacent to the chamber 31, .a seat bushing 33 orice slit 44 into the passageway 45 and the channel 4| in the seat bushing and from there through the p orts 42 and 42' into'the working chambers 34 and 34'. Upon rotation of the cylinder structure in the opposite direction, the flow of the displaced fluid will be in reverse direction through the path just traced, the resistance to suchflow and therefore the hydraulic control ofy the rotation of the wheel supporting structure being determined by the size of the orifice passageway presented .by th orifice slit 44.

I have shown a thermostat coil 46 secured Aat its inner lend to the valve plugand at its outer sion 3| thereon, the outer end of the shaft having is secured in the bore 35, the bushing being bored to receive the cylindrical valve plug 40. The seat bushing has the circumferential channel 4| communicating with the working chambers34and 34 through passageways 42 and 42' in piston hub:

At its inner end the ,valve plug 4|l hasthe passageway or bore 43 therethroughcommunieating with the chamber 31, and the valve plug has the circumferentially'extending orifice slit 44 communicating with the passageway 45 between the seat bushing channel 4| and the bushing bore in which the valve plug seats, the circumferential extent of overlap of the `passageway 45 by thei orifice slit 44 determining the resistance to the fluid ow between the shock absorbing hydraulic chambers. When the cylinder structure from which the wheel W extendsiis rotated in one direction relative to the piston structure, the displaced fluid will flow from the working chambers 33 and 33' through the ports 38 and 38 into the chamber 31 and then through the valve plug bore and the exposed part of the end to the stem 41 which extends through the piston shaft bore to the exterior thereof and there provided with a lever 48 whereby the stem struc-v ture may be manually adjusted for the desired degree of exposure of the orifice slit and the desired shock absorbing resistance. After manual setting of the valve, the'thermostat coil will respond to temperature change within the shock absorber structure so that the orifice exposure will be thermostatically adjusted to compensate for change in viscosity of the hydraulic fluid due t0 temperature change.

As shown, suitable guide washer or collar structure 48 is clamped in the bore 35 by a plug 50 for holding the stem 41 against movement 'after manual rotation thereof for adjustment for orice size. 'I'he end of the piston shaft and the stem structure adjusting lever 48 thereon. is between the fork arms' of the wheel W to be protected but to be accessible for adjustment of the valve structure. The outer end oi.' the piston shaft extending through the bearing extension 3| has packing material 5| applied thereto by a gland 52, the packing tending to prevent leakage of hydraulic fluid outwardly along the shaft.

The hydraulic working chambers of the shock absorber structure must be kept filled with hydraulic fluid whether the shock absorber is in more or less vertical position during4 operation of the landing gear, or in horizontal or more or less inverted position when the landing gear is in its withdrawn or inoperativeposition. To accomplish this I provide replenishing structure comprising a replenishing chamber proper and a replenishing compensating chamber. Referring to Figure 3, the strut I0 is provided with a cross enlarged heads 59 to besurrounded by the spring so as to keep thespringaxially aligned. Extending upwardly from the shock absorber inner wall 2| are a number of` stop pins 60 which linut the outward movement of the washer structure P. The space between the washer structure and the wall 2| constitutes the compensating chamber proper C, while the space between the washer structure and the wall 53 constitutes the replenishing compensating chamber C'. y

For controlling the flow of replenishing fluid from the chamber C to the shock absorber working chamber, check valves 6| are provided. In the wall 2|, two valve chambers 52 are provided for the check valves, and ports 53 and 53' connect these valve chambers with the hydraulic working chambers 33 and 34 respectively, Figures 3, 4

and 6. Each valve 6I is shown in the form of adisk provided with an annular seating lip or flange 64 for seating against the bottom of the valve chamber 62 for closure of the corresponding valve chamber for seating a spring 61 abutting vthe valve to holdit normally closed, the plug having a fluid passageway 6B therethrough.

A ller plug 69 is provided for the replenishing chamber C, this plug being of any well known leak proof and pressure type so that hydraulic uid may be forced therethrough under pressure into the chamber C. When such uid is forced into the chamber C under pressure, the piston or washer structure P will be shifted outwardly against the resistance of l,the spring 58 and the fluid in the chamber C will then be under pressure at all times during'the operation of the shock absorber structure. Any leakage from the hydraulic working chambers will be compensated for by fluid forced from the chamber Cpastthe check valves El, but whenever the uid in the working chambers 33 or 34' is under pressure, the check valves 6I will be held closed by the pressure so that the working chamber fluid cannot be dis# charged into the compensating chamber C.

The replenishing compensating chamber C' does not receive uid when the chamber C is charged with fluid under pressure, but the chamber C is provided with an outlet. 1D controlled by a check valve 1I, through which outlet air may escape from the chamber C' while the chamber C is being filled with fluid. Any fluid or any air which may leak past the washer structure struction, arrangement, and operation shown and described, as changes and modifications are possible which would still come within the scope of the invention.

I claim as follows:

1. An airplane supporting structure comprising a frame, a tubular strut supported on said frame for rotation on its longitudinal axis and terminating in a caster f ork journalling a wheel, hydraulic' shock absorbing structure above the fork and for" which the end portion of said tubular strut provides a cylinder wall, cross walls in said cylinder wall defining therewith a cylindrical hydraulic working space, a piston shaft coaxial with said working space and journalled in said cross walls, a piston on said'shaft within said working space, means connecting* said shaft to said framefor holding said piston shaft against rotation whereby rotation of said strut with the caster fork will cause displacement of hydraulic fluid in said working space, and means resisting the ow vof fork movement to prevent shimmying thereof.

2. An airplane supporting structure comprising a frame, a rotatable tubular supporting strut mounted on said frame and terminating in a caster fork journalling a ground engaging wheel, the end of said tubular strut above said caster I fork providing a hydraulic cylinder wall, cross P into the chamber C will therefore be expelled through the outlet 'lll so that the structure P may properly function. Should fluid leakage from the shock absorber structure take place, the washer structure P will be moved inwardly by the spring 58 to compensate for the leakage and maintain the fluid pressure within the shock absorber, vand when the structure P reaches the stop pins 60, the chamber will have to be given another charge .of fluid. With the uid in the chamber at all times under pressure, the hydraulic working chamber will be kept properly replenished and filled at all times independently of the position of the shock absorber, and the shock absorber will therefore always be ready for efflcient operation when the landing gear is to be used.

I have shown a uid intercepting channel 12 in the bearing wall 25 for the shock absorber piston shaft and a passageway for returning the intercepted leakage fluid through the reservoir or'replenishing chamber C'. This passageway includes the passage 13 in the wall 25, the bore 21 I. of one of the pins 21, and the passage 14 through the corresponding partition wall 23. Any uid forced out along the piston shaft by the pressure within the working chamber is thus intercepted and returned to the replenishing chamber C.

I thus provide simple and efficient shock aby sorber structure and arrangement particularly adaptable for preventing shimmy or wobble of landing gear wheels without interfering with the eiiicient operation and functioning of the wheels, and with the shock absorber assembly concealed and protected but readily accessible for adjustment.

I do not desire to be limited to the exact conwalls in said cylinder wall defining therewith a hydraulic cylinder, a piston shaft coaxial with said 'thedisplaced fluid whereby to dampen the caster cylinder and journalled in said cross walls, vanes von said shaft within said cylinder, said shaft projecti g from the lower end of said strut, means connecting the projecting end of said shaft to said frame ,for holding the shaft against rota1 tional movement whereby rotational movement of said strut with the caster fork will cause displacement of hydraulic fluid in said cylinder, and valve means for controlling the fluid flow for dampening of the caster movement whereby to prevent shimmying.

3. An airplane supporting structure comprising a frame, a cylinder supported on said frame for rotation on its axis, a caster forksecured to and extending downwardly from said cylinder and journalling a wheel, baiiie walls extending radially inwardly in said cylinder, a shaft extending 'axially through said cylinder and having' radial.

draulic nuid in said cylinder wi11 be displaced,-

and adjustable means for regulating the flow of the displaced uid whereby to dampen the caster movement and prevent shimmying.

4. An airplane landing gear comprising a frame, a cylinder forming part of a rotatable strut mounted on said frame, a caster fork secured to and extending from the lower end of said cylinder and journaling a ground engaging wheel, baille walls extending inwardly in said cylinder, a shaft coaxial with said cylinder and having radial baiile walls intermediate said cylinder baille walls to define therewith hydraulic working chambers for containing hydraulic fluid,

means on said frame holding said shaft against rotationv with said cylinder, rotation of said caster fork and cylinderl relative to said 'held shaft causing displacement of hydraulic fluid in said working chambers, and'adjustable means vfor dampen the rotation of said cylinder and caster 4controlling the displacement flow to thereby` 5. An airplane landing gear comprising a frame, a rotatable tubular` supporting strut on said frame terminating in a caster fork secured thereto and journalling a wheel, crosswalls in the lower en d of said strut dening with the surrounding tubular wall of the strut a hydraulic working space,

bame walls extending into said space from the tubular wall, av shaft extending through said cylinder space concentric therewith and having radial baille walls intermediate the baille wall oi said tubular wall to denne therewith hydraulic working chambers containing hydraulic 1luid, means connecting said shaft to said frame for holding said shaft' against rotary movement s whereby upon rotary movement of said strut with said caster fork fluid in said working chambers will be displaced, and valve means for-restricting the iiow of the displaced fluid whereby to dampen the caster movement and prevent shimmying.

6. An airplane landing gear comprising a frame,

.a rotatable tubular supporting strut on said frame terminating in a cast-er fork secured thereto andA journalling a wheel, cross walls in the lower end of said strut' defining with the surrounding tubular wall of the strut a. hydraulic working space, baille walls extending into said space from the tur bular walls, a shaft extending through said cylinder space concentric therewith and having radial baille walls intermediate the baille wall of said tubular wall to'dene therewith hydraulic working chamberscontaining hydraulic fluid, means connecting said shaft to said frame for holding said 'shaft against rotary movement whereby upon rotary movement of said strut with said caster fork fluid in said'working chambers will be displaced, valvemeans for restricting the flow of the displaced fiuid whereby to dampen the caster movement and prevent shimmying, a hydraulic reservoir chamber within said strut above said working` chambers, check valve control passageways between said reservoir chamber and said working chambers, and a spring pressed plunger structure in said reservoir chamber operable to force iluid therefrom through said passageways to keep said working chambers lled at all times with hydraulic fluids.

7. An anti-shimmy arrangement for a castering wheel of a flying machine landing gear comprising, a strut which may be mounted, for rotation about its longitudinal axis, on the flying l 'machina an element adapted to carry a ground 

